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42 Fbrging-Stamping - Heat Treating
low upkeep cost usually is on the side of the electric
furnace. To this may be added automatic control of
temperatures, duplication of heating cycles, reduction
in defective heat-treated parts, and usually many other
influencing factors which work in the direction of a
reduced "over all" cost of production in favor of the
electric heat-treating furnace.
The Metallic Resistor Furnace.
Important heat-treating processes, in which the
metallurgist should be interested, and for which the
metallic resistor electric furnace is peculiarly adapted,
will be enumerated and briefly described so that the
working field for such type of furnace may be clearly
indicated. We may, for convenience, consider elec-
February, 1925
the carbon content, and the spread of the critical range
varies likewise.
The committee of the American Society of Testing
Materials has recommended the following range in
temperatures:
Carbon Content Annealing Temp. Range
Per Cent Degrees Fahr.
Less than 0.12 1607 to 1697
0.12 to 0.25 1544 to 1598
0.30 to 0.49 1399 to 1544
0.50 to 1.00 1454 to 1499
The length of time steel should be held at the annealing
temperature varies with the size and shape of
the piece. It is important that the piece be heated
through uniformly at the annealing temperature.
Where quality of output is the watchword, modern
heat treatment is not attempted without first carrying
out correct annealing treatments as a proper foundation
for subsequent processes.
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